PRF/J: Regulation of Phytophagus Insect Populations: Density Perturbation Experiments on Microrhopala vittata, an Herbivore of Solidago

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It has long been debated whether populations of phytophagous insects are regulated by density-dependent processes acting to return their densities to equilibrium levels, or whether they are characterized instead by non-equilibrium processes such as local extinction and recolonization. This question will be addressed by performing density-perturbation experiments on Microrhopala vittata, a leaf-mining beetle that feeds on goldenrod (Solidago spp.). Work will commence with assessments of density, mortality and fecundity of this beetle in several small (1000 stems) stands of goldenrod. Populations will then have their density experimentally supplemented (to levels 10-20% below the minimum observed), and the effect of these manipulations on predation, parasitism, fecundity and dispersal will be quantified. All samples for mortality and fecundity will be done non-destructively (no Microrhopala or enemies will be killed) so that quantification of these processes will not affect population density. A return of Microrhopala density to more moderate levels following perturbations will support the equilibrium viewpoint. Alternatively, supplemented populations may irrupt and reduced populations may become locally extinct; this would constitute evidence for the non-equilibrium viewpoint. Funding is being awarded for two years of postdoctoral fellowship research at The University of Quebec in Montreal, Canada.